Front end systems with switched termination for enhanced intermodulation distortion performance

ABSTRACT

Front end systems with switched termination for enhanced intermodulation distortion performance are provided herein. The switched termination can be used on transmit paths and/or receive paths of the front end system to suppress impedance variation when the signal paths are inactive. For example, with respect to switched termination for transmit paths, a front end system can include a frequency multiplexing circuit connected to a band switch by a first radio frequency (RF) signal path and by a second RF signal path. The band switch selectively provides the frequency multiplexing circuit with a first transmit signal over the first RF signal path and with a second transmit signal over the second RF signal path. The front end system further includes a switched termination circuit in shunt with the first RF signal path and operable to turn on to suppress impedance variation when the first RF signal path is inactive.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Patent Application No. 62/664,588, filed Apr. 30, 2018,and entitled “FRONT END SYSTEMS WITH SWITCHED TERMINATION FOR ENHANCEDINTERMODULATION DISTORTION PERFORMANCE,” which is herein incorporated byreference in its entirety.

BACKGROUND Field

Embodiments of the invention relate to electronic systems, and inparticular, to radio frequency electronics.

Description of Related Technology

Radio frequency (RF) communication systems can be used for transmittingand/or receiving signals of a wide range of frequencies. For example, anRF communication system can be used to wirelessly communicate RF signalsin a frequency range of about 30 kHz to 300 GHz, such as in the range ofabout 450 MHz to about 7 GHz for certain communications standards.

Examples of RF communication systems include, but are not limited to,mobile phones, tablets, base stations, network access points,customer-premises equipment (CPE), laptops, and wearable electronics.

SUMMARY

In certain embodiments, the present disclosure relates to a front endsystem. The front end system includes a frequency multiplexing circuit,a band switch configured to selectively provide the frequencymultiplexing circuit with a first transmit signal over a first radiofrequency signal path and with a second transmit signal over a secondradio frequency signal path, and a first switched termination circuit inshunt with the first radio frequency signal path and operable to turn onto suppress impedance variation when the first radio frequency signalpath is inactive.

In some embodiments, the front end system further includes a secondswitched termination circuit in shunt with the second radio frequencysignal path and operable to turn on to suppress impedance variation whenthe second radio frequency signal path is inactive.

In a number of embodiments, the front end system further includes anantenna switch coupled to the frequency multiplexing circuit at a node,and the first switched termination circuit is operable to maintainimpedance matching at the node over a signal frequency range of thefirst transmit signal.

In various embodiments, the frequency multiplexing circuit is furtherconfigured to output a first receive signal and a second receive signal.

In some embodiments, the first transmit signal is a band 1 signal andthe second transmit signal is a band 3 signal.

In a number of embodiments, the first transmit signal is a band 3 signaland the second transmit signal is a band 1 signal.

In several embodiments, the frequency multiplexing circuit includes atleast one duplexer.

In various embodiments, the frequency multiplexing circuit includes atleast one quadplexer.

In some embodiments, the band switch provides the first radio frequencysignal at an output terminal, and the front end system further includesa grounding switch electrically connected between the output terminaland ground. According to a number of embodiments, the front end systemfurther includes a decoupling switch electrically connected between theoutput terminal of the band switch and the first switched terminationcircuit.

In various embodiments, the first switched termination circuit includesa shunt switch and a termination resistor electrically connected inseries. According to a number of embodiments, the termination resistorhas a resistance of about fifty ohms.

In several embodiments, the band switch is further configured toselectively provide the frequency multiplexing circuit with a thirdtransmit signal over a third radio frequency signal path.

In some embodiments, the front end system further includes a poweramplifier configured to provide the band switch with the first transmitsignal and the second transmit signal at an input terminal to the bandswitch.

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes a transceiver configured to generateat least one radio frequency signal, and a front end system configuredto process the at least one radio frequency signal from the transceiverto generate a first transmit signal and a second transmit signal. Thefront end system includes a frequency multiplexing circuit and a bandswitch configured to selectively provide the frequency multiplexingcircuit with the first transmit signal over a first radio frequencysignal path and with the second transmit signal over a second radiofrequency signal path. The front end system further includes a firstswitched termination circuit in shunt with the first radio frequencysignal path and operable to turn on to suppress impedance variation whenthe first radio frequency signal path is inactive.

In some embodiments, the front end system further includes a secondswitched termination circuit in shunt with the second radio frequencysignal path and operable to turn on to suppress impedance variation whenthe second radio frequency signal path is inactive.

In a number of embodiments, the front end system further includes anantenna switch coupled to the frequency multiplexing circuit at a node,and the first switched termination circuit is operable to maintainimpedance matching at the node over a signal frequency range of thefirst transmit signal. According to various embodiments, the mobiledevice further includes a first antenna, and the antenna switch isoperable to selectively connect the node to the first antenna.

In several embodiments, the front end system further includes at leastone power amplifier configured to generate the first transmit signal andthe second transmit signal.

In some embodiments, the band switch provides the first radio frequencysignal at an output terminal, and the front end system further includesa grounding switch electrically connected between the output terminaland ground. According to a number of embodiments, the front end systemfurther includes a decoupling switch electrically connected between theoutput terminal of the band switch and the first switched terminationcircuit.

In certain embodiments, the present disclosure relates to a method ofradio frequency signal communication. The method includes controlling astate of a band switch to provide a first transmit signal to a frequencymultiplexing circuit over a first radio frequency signal path, changingthe state of the band switch to deactivate the first radio frequencysignal path and to provide a second transmit signal to the frequencymultiplexing circuit over a second radio frequency signal path, andturning on a first switched termination circuit in shunt to the firstradio frequency signal path to suppress impedance variation when thefirst radio frequency signal path is deactivated.

In a number of embodiments, the method further includes maintainingimpedance matching at a node between the frequency multiplexing circuitand an antenna switch over a signal frequency range of the firsttransmit signal.

In certain embodiments, the present disclosure relates to a front endsystem. The front end system includes a frequency multiplexing circuit,a first low noise amplifier electrically connected to the frequencymultiplexing circuit over a first radio frequency signal path, a secondlow noise amplifier electrically connected to the frequency multiplexingcircuit over a second radio frequency signal path, and a first switchedtermination circuit in shunt with the first radio frequency signal pathand operable to turn on to suppress impedance variation when the firstlow noise amplifier is inactive.

In some embodiments, the front end system further includes a secondswitched termination circuit in shunt with the second radio frequencysignal path and operable to turn on to suppress impedance variation whenthe second low noise amplifier is inactive.

In several embodiments, the front end system further includes an antennaswitch coupled to the frequency multiplexing circuit at a node, and thefirst switched termination circuit is operable to maintain impedancematching at the node over a signal frequency range of a radio frequencysignal amplified by the first low noise amplifier.

In a number of embodiments, the frequency multiplexing circuit includesat least one duplexer.

In various embodiments, the front end system further includes agrounding switch electrically connected between an input terminal of thefirst low noise amplifier and ground. According to several embodiments,the front end system further includes a decoupling switch electricallyconnected between the input terminal of the first low noise amplifierand the first switched termination circuit.

In some embodiments, the first switched termination circuit includes ashunt switch and a termination resistor electrically connected inseries. According to various embodiments, the termination resistor has aresistance of about fifty ohms.

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes an antenna, and a front end systemelectrically coupled to the antenna. The front end system includes afrequency multiplexing circuit, a first low noise amplifier electricallyconnected to the frequency multiplexing circuit over a first radiofrequency signal path, a second low noise amplifier electricallyconnected to the frequency multiplexing circuit over a second radiofrequency signal path, and a first switched termination circuit in shuntwith the first radio frequency signal path and operable to turn on tosuppress impedance variation when the first low noise amplifier isinactive.

In some embodiments, the front end system further includes a secondswitched termination circuit in shunt with the second radio frequencysignal path and operable to turn on to suppress impedance variation whenthe second low noise amplifier is inactive. According to a number ofembodiments, the front end system further includes an antenna switchcoupled to the frequency multiplexing circuit at a node, and the firstswitched termination circuit is operable to maintain impedance matchingat the node over a signal frequency range of a radio frequency signalamplified by the first low noise amplifier.

In various embodiments, the frequency multiplexing circuit includes atleast one duplexer.

In some embodiments, the front end system further includes a groundingswitch electrically connected between an input terminal of the first lownoise amplifier and ground. According to a number of embodiments, thefront end system further includes decoupling switch electricallyconnected between the input terminal of the first low noise amplifierand the first switched termination circuit.

In several embodiments, the first switched termination circuit includesa shunt switch and a termination resistor electrically connected inseries. In accordance with various embodiments, the termination resistorhas a resistance of about fifty ohms.

In certain embodiments, the present disclosure relates to a method ofradio frequency signal communication. The method includes providing afirst receive signal from a frequency multiplexing circuit to a firstlow noise amplifier over a first radio frequency signal path, providinga second receive signal from the frequency multiplexing circuit to asecond low noise amplifier over a second radio frequency signal path,and turning on a first switched termination circuit in shunt to thefirst radio frequency signal path to suppress impedance variation whenthe first low noise amplifier is deactivated.

In some embodiments, the method further includes maintaining impedancematching at a node between the frequency multiplexing circuit and anantenna switch over a signal frequency range of the first receivesignal.

In various embodiments, the method further includes grounding an inputterminal of the first low noise amplifier using a grounding switch whenthe first low noise amplifier is deactivated. According to severalembodiments, the method further includes decoupling the input terminalof the first low noise amplifier and the first switched terminationcircuit using a decoupling switch when the first low noise amplifier isdeactivated.

In certain embodiments, the present disclosure relates to a front endsystem. The front end system includes a frequency multiplexing circuit,a receive switch configured to receive a first receive signal from thefrequency multiplexing circuit over a first radio frequency signal pathand to receive a second receive signal from the frequency multiplexingcircuit over a second radio frequency signal path, and a first switchedtermination circuit in shunt with the first radio frequency signal pathand operable to turn on to suppress impedance variation when the firstradio frequency signal path is inactive.

In several embodiments, the front end system further includes a secondswitched termination circuit in shunt with the second radio frequencysignal path and operable to turn on to suppress impedance variation whenthe second radio frequency signal path is inactive.

In some embodiments, the front end system further includes an antennaswitch coupled to the frequency multiplexing circuit at a node, and thefirst switched termination circuit is operable to maintain impedancematching at the node over a signal frequency range of the first receivesignal.

In various embodiments, the frequency multiplexing circuit includes atleast one duplexer.

In several embodiments, the front end system further includes agrounding switch electrically connected between an input terminal of thereceive switch and ground. According to a number of embodiments, thefront end system further includes a decoupling switch electricallyconnected between the input terminal of the first low noise amplifierand the first switched termination circuit.

In some embodiments, the first switched termination circuit includes ashunt switch and a termination resistor electrically connected inseries. According to various embodiments, the termination resistor has aresistance of about fifty ohms.

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes an antenna, and a front end systemelectrically coupled to the antenna. The front end system includes afrequency multiplexing circuit, a receive switch configured to receive afirst receive signal from the frequency multiplexing circuit over afirst radio frequency signal path and to receive a second receive signalfrom the frequency multiplexing circuit over a second radio frequencysignal path, and a first switched termination circuit in shunt with thefirst radio frequency signal path and operable to turn on to suppressimpedance variation when the first radio frequency signal path isinactive.

In some embodiments, the front end system further includes a secondswitched termination circuit in shunt with the second radio frequencysignal path and operable to turn on to suppress impedance variation whenthe second radio frequency signal path is inactive.

In a number of embodiments, the front end system further includes anantenna switch coupled to the frequency multiplexing circuit at a node,and the first switched termination circuit is operable to maintainimpedance matching at the node over a signal frequency range of a radiofrequency signal amplified by the first low noise amplifier.

In various embodiments, the frequency multiplexing circuit includes atleast one duplexer.

In several embodiments, the front end system further includes agrounding switch electrically connected between an input terminal of thereceive switch and ground. According to a number of embodiments, thefront end system further includes a decoupling switch electricallyconnected between the input terminal and the first switched terminationcircuit.

In some embodiments, the first switched termination circuit includes ashunt switch and a termination resistor electrically connected inseries. According to a number of embodiments, the termination resistorhas a resistance of about fifty ohms.

In certain embodiments, the present disclosure relates to a method ofradio frequency signal communication. The method includes providing afirst receive signal from a frequency multiplexing circuit to a receiveswitch over a first radio frequency signal path, providing a secondreceive signal from the frequency multiplexing circuit to the receiveswitch over a second radio frequency signal path, and turning on a firstswitched termination circuit in shunt to the first radio frequencysignal path to suppress impedance variation when the first radiofrequency signal path is deactivated.

In some embodiments, the method further includes maintaining impedancematching at a node between the frequency multiplexing circuit and anantenna switch over a signal frequency range of the first receivesignal.

In various embodiments, the method further includes grounding an inputterminal of the receive switch using a grounding switch when the firstradio frequency signal path is deactivated. According to severalembodiments, the method further includes decoupling the input terminalof the receive switch and the first switched termination circuit using adecoupling switch when the first radio frequency signal path isdeactivated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one example of a communication network.

FIG. 2A is a schematic diagram of one example of a communication linkusing carrier aggregation.

FIG. 2B illustrates various examples of uplink carrier aggregation forthe communication link of FIG. 2A.

FIG. 2C illustrates various examples of downlink carrier aggregation forthe communication link of FIG. 2A.

FIG. 3A is a schematic diagram of a front end system with switchedtermination according to one embodiment.

FIG. 3B is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 3C is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 3D is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 3E is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 4A is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 4B is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 5A is one example of a Smith chart for a front end system withoutswitched termination.

FIG. 5B is one example of a Smith chart for a front end system withswitched termination.

FIG. 6 is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 7A is a schematic diagram of one embodiment of a switchconfiguration for a terminal of a band switch.

FIG. 7B is a schematic diagram of another embodiment of a switchconfiguration for a terminal of a band switch.

FIG. 8 is a schematic diagram of a front end system with switchedtermination according to another embodiment.

FIG. 9 is a schematic diagram of one embodiment of a mobile device.

DETAILED DESCRIPTION OF EMBODIMENTS

The following detailed description of certain embodiments presentsvarious descriptions of specific embodiments. However, the innovationsdescribed herein can be embodied in a multitude of different ways, forexample, as defined and covered by the claims. In this description,reference is made to the drawings where like reference numerals canindicate identical or functionally similar elements. It will beunderstood that elements illustrated in the figures are not necessarilydrawn to scale. Moreover, it will be understood that certain embodimentscan include more elements than illustrated in a drawing and/or a subsetof the elements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

The International Telecommunication Union (ITU) is a specialized agencyof the United Nations (UN) responsible for global issues concerninginformation and communication technologies, including the shared globaluse of radio spectrum.

The 3rd Generation Partnership Project (3GPP) is a collaboration betweengroups of telecommunications standard bodies across the world, such asthe Association of Radio Industries and Businesses (ARIB), theTelecommunications Technology Committee (TTC), the China CommunicationsStandards Association (CCSA), the Alliance for TelecommunicationsIndustry Solutions (ATIS), the Telecommunications Technology Association(TTA), the European Telecommunications Standards Institute (ETSI), andthe Telecommunications Standards Development Society, India (TSDSI).

Working within the scope of the ITU, 3GPP develops and maintainstechnical specifications for a variety of mobile communicationtechnologies, including, for example, second generation (2G) technology(for instance, Global System for Mobile Communications (GSM) andEnhanced Data Rates for GSM Evolution (EDGE)), third generation (3G)technology (for instance, Universal Mobile Telecommunications System(UMTS) and High Speed Packet Access (HSPA)), and fourth generation (4G)technology (for instance, Long Term Evolution (LTE) and LTE-Advanced).

The technical specifications controlled by 3GPP can be expanded andrevised by specification releases, which can span multiple years andspecify a breadth of new features and evolutions.

In one example, 3GPP introduced carrier aggregation (CA) for LTE inRelease 10. Although initially introduced with two downlink carriers,3GPP expanded carrier aggregation in Release 14 to include up to fivedownlink carriers and up to three uplink carriers. Other examples of newfeatures and evolutions provided by 3GPP releases include, but are notlimited to, License Assisted Access (LAA), enhanced LAA (eLAA),Narrowband Internet of things (NB-IOT), Vehicle-to-Everything (V2X), andHigh Power User Equipment (HPUE).

3GPP introduced Phase 1 of fifth generation (5G) technology in Release15, and plans to introduce Phase 2 of 5G technology in Release 16(targeted for 2019). Subsequent 3GPP releases will further evolve andexpand 5G technology. 5G technology is also referred to herein as 5G NewRadio (NR).

5G NR supports or plans to support a variety of features, such ascommunications over millimeter wave spectrum, beamforming capability,high spectral efficiency waveforms, low latency communications, multipleradio numerology, and/or non-orthogonal multiple access (NOMA). Althoughsuch RF functionalities offer flexibility to networks and enhance userdata rates, supporting such features can pose a number of technicalchallenges.

The teachings herein are applicable to a wide variety of communicationsystems, including, but not limited to, communication systems usingadvanced cellular technologies, such as LTE-Advanced, LTE-Advanced Pro,and/or 5G NR.

FIG. 1 is a schematic diagram of one example of a communication network10. The communication network 10 includes a macro cell base station 1, asmall cell base station 3, and various examples of user equipment (UE),including a first mobile device 2 a, a wireless-connected car 2 b, alaptop 2 c, a stationary wireless device 2 d, a wireless-connected train2 e, a second mobile device 2 f, and a third mobile device 2 g.

Although specific examples of base stations and user equipment areillustrated in FIG. 1, a communication network can include base stationsand user equipment of a wide variety of types and/or numbers.

For instance, in the example shown, the communication network 10includes the macro cell base station 1 and the small cell base station3. The small cell base station 3 can operate with relatively lowerpower, shorter range, and/or with fewer concurrent users relative to themacro cell base station 1. The small cell base station 3 can also bereferred to as a femtocell, a picocell, or a microcell. Although thecommunication network 10 is illustrated as including two base stations,the communication network 10 can be implemented to include more or fewerbase stations and/or base stations of other types.

Although various examples of user equipment are shown, the teachingsherein are applicable to a wide variety of user equipment, including,but not limited to, mobile phones, tablets, laptops, IoT devices,wearable electronics, customer premises equipment (CPE),wireless-connected vehicles, wireless relays, and/or a wide variety ofother communication devices. Furthermore, user equipment includes notonly currently available communication devices that operate in acellular network, but also subsequently developed communication devicesthat will be readily implementable with the inventive systems,processes, methods, and devices as described and claimed herein.

The illustrated communication network 10 of FIG. 1 supportscommunications using a variety of cellular technologies, including, forexample, 4G LTE and 5G NR. In certain implementations, the communicationnetwork 10 is further adapted to provide a wireless local area network(WLAN), such as WiFi. Although various examples of communicationtechnologies have been provided, the communication network 10 can beadapted to support a wide variety of communication technologies.

Various communication links of the communication network 10 have beendepicted in FIG. 1. The communication links can be duplexed in a widevariety of ways, including, for example, using frequency-divisionduplexing (FDD) and/or time-division duplexing (TDD). FDD is a type ofradio frequency communications that uses different frequencies fortransmitting and receiving signals. FDD can provide a number ofadvantages, such as high data rates and low latency. In contrast, TDD isa type of radio frequency communications that uses about the samefrequency for transmitting and receiving signals, and in which transmitand receive communications are switched in time. TDD can provide anumber of advantages, such as efficient use of spectrum and variableallocation of throughput between transmit and receive directions.

In certain implementations, user equipment can communicate with a basestation using one or more of 4G LTE, 5G NR, and WiFi technologies. Incertain implementations, enhanced license assisted access (eLAA) is usedto aggregate one or more licensed frequency carriers (for instance,licensed 4G LTE and/or 5G NR frequencies), with one or more unlicensedcarriers (for instance, unlicensed WiFi frequencies).

As shown in FIG. 1, the communication links include not onlycommunication links between UE and base stations, but also UE to UEcommunications and base station to base station communications. Forexample, the communication network 10 can be implemented to supportself-fronthaul and/or self-backhaul.

The communication links can operate over a wide variety of frequencies.In certain implementations, communications are supported using 5G NRtechnology over one or more frequency bands that are less than 6Gigahertz (GHz) and/or over one or more frequency bands that are greaterthan 6 GHz. For example, the communication links can serve FrequencyRange 1 (FR1), Frequency Range 2 (FR2), or a combination thereof. In oneembodiment, one or more of the mobile devices support a HPUE power classspecification.

In certain implementations, a base station and/or user equipmentcommunicates using beamforming. For example, beamforming can be used tofocus signal strength to overcome path losses, such as high lossassociated with communicating over high signal frequencies. In certainembodiments, user equipment, such as one or more mobile phones,communicate using beamforming on millimeter wave frequency bands in therange of 30 GHz to 300 GHz and/or upper centimeter wave frequencies inthe range of 6 GHz to 30 GHz, or more particularly, 24 GHz to 30 GHz.

Different users of the communication network 10 can share availablenetwork resources, such as available frequency spectrum, in a widevariety of ways.

In one example, frequency division multiple access (FDMA) is used todivide a frequency band into multiple frequency carriers. Additionally,one or more carriers are allocated to a particular user. Examples ofFDMA include, but are not limited to, single carrier FDMA (SC-FDMA) andorthogonal FDMA (OFDMA). OFDMA is a multicarrier technology thatsubdivides the available bandwidth into multiple mutually orthogonalnarrowband subcarriers, which can be separately assigned to differentusers.

Other examples of shared access include, but are not limited to, timedivision multiple access (TDMA) in which a user is allocated particulartime slots for using a frequency resource, code division multiple access(CDMA) in which a frequency resource is shared amongst different usersby assigning each user a unique code, space-divisional multiple access(SDMA) in which beamforming is used to provide shared access by spatialdivision, and non-orthogonal multiple access (NOMA) in which the powerdomain is used for multiple access. For example, NOMA can be used toserve multiple users at the same frequency, time, and/or code, but withdifferent power levels.

Enhanced mobile broadband (eMBB) refers to technology for growing systemcapacity of LTE networks. For example, eMBB can refer to communicationswith a peak data rate of at least 10 Gbps and a minimum of 100 Mbps foreach user. Ultra-reliable low latency communications (uRLLC) refers totechnology for communication with very low latency, for instance, lessthan 2 milliseconds. uRLLC can be used for mission-criticalcommunications such as for autonomous driving and/or remote surgeryapplications. Massive machine-type communications (mMTC) refers to lowcost and low data rate communications associated with wirelessconnections to everyday objects, such as those associated with Internetof Things (IoT) applications.

The communication network 10 of FIG. 1 can be used to support a widevariety of advanced communication features, including, but not limitedto, eMBB, uRLLC, and/or mMTC.

FIG. 2A is a schematic diagram of one example of a communication linkusing carrier aggregation. Carrier aggregation can be used to widenbandwidth of the communication link by supporting communications overmultiple frequency carriers, thereby increasing user data rates andenhancing network capacity by utilizing fragmented spectrum allocations.

In the illustrated example, the communication link is provided between abase station 21 and a mobile device 22. As shown in FIG. 2A, thecommunications link includes a downlink channel used for RFcommunications from the base station 21 to the mobile device 22, and anuplink channel used for RF communications from the mobile device 22 tothe base station 21.

Although FIG. 2A illustrates carrier aggregation in the context of FDDcommunications, carrier aggregation can also be used for TDDcommunications.

In certain implementations, a communication link can provideasymmetrical data rates for a downlink channel and an uplink channel.For example, a communication link can be used to support a relativelyhigh downlink data rate to enable high speed streaming of multimediacontent to a mobile device, while providing a relatively slower datarate for uploading data from the mobile device to the cloud.

In the illustrated example, the base station 21 and the mobile device 22communicate via carrier aggregation, which can be used to selectivelyincrease bandwidth of the communication link. Carrier aggregationincludes contiguous aggregation, in which contiguous carriers within thesame operating frequency band are aggregated. Carrier aggregation canalso be non-contiguous, and can include carriers separated in frequencywithin a common band or in different bands.

In the example shown in FIG. 2A, the uplink channel includes threeaggregated component carriers full, f_(UL1), f_(UL2), and f_(UL3).Additionally, the downlink channel includes five aggregated componentcarriers f_(DL1), f_(DL2), f_(DL3), f_(DL4), and f_(DL5). Although oneexample of component carrier aggregation is shown, more or fewercarriers can be aggregated for uplink and/or downlink. Moreover, anumber of aggregated carriers can be varied over time to achieve desireduplink and downlink data rates.

For example, a number of aggregated carriers for uplink and/or downlinkcommunications with respect to a particular mobile device can changeover time. For example, the number of aggregated carriers can change asthe device moves through the communication network and/or as networkusage changes over time.

FIG. 2B illustrates various examples of uplink carrier aggregation forthe communication link of FIG. 2A. FIG. 2B includes a first carrieraggregation scenario 31, a second carrier aggregation scenario 32, and athird carrier aggregation scenario 33, which schematically depict threetypes of carrier aggregation.

The carrier aggregation scenarios 31-33 illustrate different spectrumallocations for a first component carrier full, a second componentcarrier f_(UL2), and a third component carrier f_(UL3). Although FIG. 2Bis illustrated in the context of aggregating three component carriers,carrier aggregation can be used to aggregate more or fewer carriers.Moreover, although illustrated in the context of uplink, the aggregationscenarios are also applicable to downlink.

The first carrier aggregation scenario 31 illustrates intra-bandcontiguous carrier aggregation, in which component carriers that areadjacent in frequency and in a common frequency band are aggregated. Forexample, the first carrier aggregation scenario 31 depicts aggregationof component carriers f_(UL1), f_(UL2), and f_(UL3) that are contiguousand located within a first frequency band BAND1.

With continuing reference to FIG. 2B, the second carrier aggregationscenario 32 illustrates intra-band non-continuous carrier aggregation,in which two or more components carriers that are non-adjacent infrequency and within a common frequency band are aggregated. Forexample, the second carrier aggregation scenario 32 depicts aggregationof component carriers f_(UL1), f_(UL2), and f_(UL3) that arenon-contiguous, but located within a first frequency band BAND1.

The third carrier aggregation scenario 33 illustrates inter-bandnon-contiguous carrier aggregation, in which component carriers that arenon-adjacent in frequency and in multiple frequency bands areaggregated. For example, the third carrier aggregation scenario 33depicts aggregation of component carriers f_(UL1) and f_(UL2) of a firstfrequency band BAND1 with component carrier f_(UL3) of a secondfrequency band BAND2.

FIG. 2C illustrates various examples of downlink carrier aggregation forthe communication link of FIG. 2A. The examples depict various carrieraggregation scenarios 34-38 for different spectrum allocations of afirst component carrier f_(DL1), a second component carrier f_(DL2), athird component carrier f_(DL3), a fourth component carrier f_(DL4), anda fifth component carrier f_(DL5). Although FIG. 2C is illustrated inthe context of aggregating five component carriers, carrier aggregationcan be used to aggregate more or fewer carriers. Moreover, althoughillustrated in the context of downlink, the aggregation scenarios arealso applicable to uplink.

The first carrier aggregation scenario 34 depicts aggregation ofcomponent carriers that are contiguous and located within the samefrequency band. Additionally, the second carrier aggregation scenario 35and the third carrier aggregation scenario 36 illustrates two examplesof aggregation that are non-contiguous, but located within the samefrequency band. Furthermore, the fourth carrier aggregation scenario 37and the fifth carrier aggregation scenario 38 illustrates two examplesof aggregation in which component carriers that are non-adjacent infrequency and in multiple frequency bands are aggregated. As a number ofaggregated component carriers increases, a complexity of possiblecarrier aggregation scenarios also increases.

With reference to FIGS. 2A-2C, the individual component carriers used incarrier aggregation can be of a variety of frequencies, including, forexample, frequency carriers in the same band or in multiple bands.Additionally, carrier aggregation is applicable to implementations inwhich the individual component carriers are of about the same bandwidthas well as to implementations in which the individual component carriershave different bandwidths.

Certain communication networks allocate a particular user device with aprimary component carrier (PCC) or anchor carrier for uplink and a PCCfor downlink. Additionally, when the mobile device communicates using asingle frequency carrier for uplink or downlink, the user devicecommunicates using the PCC. To enhance bandwidth for uplinkcommunications, the uplink PCC can be aggregated with one or more uplinksecondary component carriers (SCCs). Additionally, to enhance bandwidthfor downlink communications, the downlink PCC can be aggregated with oneor more downlink SCCs.

In certain implementations, a communication network provides a networkcell for each component carrier. Additionally, a primary cell canoperate using a PCC, while a secondary cell can operate using a SCC. Theprimary and second cells may have different coverage areas, forinstance, due to differences in frequencies of carriers and/or networkenvironment.

License assisted access (LAA) refers to downlink carrier aggregation inwhich a licensed frequency carrier associated with a mobile operator isaggregated with a frequency carrier in unlicensed spectrum, such asWiFi. LAA employs a downlink PCC in the licensed spectrum that carriescontrol and signaling information associated with the communicationlink, while unlicensed spectrum is aggregated for wider downlinkbandwidth when available. LAA can operate with dynamic adjustment ofsecondary carriers to avoid WiFi users and/or to coexist with WiFiusers. Enhanced license assisted access (eLAA) refers to an evolution ofLAA that aggregates licensed and unlicensed spectrum for both downlinkand uplink.

Overview of Front End Systems with Switched Termination

A radio frequency (RF) communication system can include a front endsystem for processing RF signals transmitted and/or received by way ofwireless communications. Examples of such RF communication systemsinclude, but are not limited to, mobile phones, tablets, base stations,network access points, customer-premises equipment (CPE), laptops, andwearable electronics.

A front end system can be implemented to support a variety of featuresfor enhancing bandwidth and/or other performance characteristics. In oneexample, a front end system is implemented to support carrieraggregation, thereby providing flexibility to increase peak data rates.In another example, a front end system is implemented to support MIMOcommunications to increase throughput and enhance mobile broadbandservice. For instance, MIMO communications benefit from higher signal tonoise ratio, improved coding, and/or reduced signal interference due tospatial multiplexing differences of the radio environment.

Although implementing a front end system to support such features canprovide a number of advantages, implementing the front end system inthis manner can give rise to a number of coexistence or interoperabilityissues.

The teachings herein seek to provide a front end system that providesnot only high isolation, but also exhibits robust intermodulationdistortion (IMD) performance, such as good second-order intercept point(IP2) and/or third-order intercept point (IP3). In contrast, certainconventional front end systems suffer from a tradeoff between IMD andisolation, such as degraded IP2 and/or IP3 performance for a givenamount of isolation.

A low impedance switch can be connected to a terminal of a band switchfor shunting an inactive transmit path to ground, thereby providing goodisolation. Although grounding an inactive transmit path can provide highisolation, the inventors have recognized that implementing the front endsystem in this manner can give rise to an impedance mismatch. Theimpedance mismatch leads to poor IMD performance, which in turn candegrade linearity and/or other performance specifications of the frontend system.

Front end systems with switched termination for enhanced intermodulationdistortion performance are provided herein. The switched termination canbe used on transmit paths and/or receive paths of the front end systemto suppress impedance variation when the signal paths are inactive.

For example, with respect to switched termination for transmit paths, afront end system can include a frequency multiplexing circuit (forinstance, duplexing circuitry) connected to a band switch by a first RFsignal path and by a second RF signal path. The band switch selectivelyprovides the frequency multiplexing circuit with a first transmit signalover the first RF signal path and with a second transmit signal over thesecond RF signal path. The front end system further includes a switchedtermination circuit in shunt with the first RF signal path and operableto turn on to suppress impedance variation when the first RF signal pathis inactive.

By implementing the front end system in this manner, a number ofadvantages are provided, such as low IMD variation versus frequency atinterfering carrier frequencies. In contrast, conventional front endarchitectures fail to appreciate an impact of impedance variationresulting from shunting an unused transmit port with zero or lowimpedance.

Moreover, preserving termination impedance can enhance the performanceof non-linear front end components, such as silicon on-insulator (SOI)switch transistors, which can be sensitive to changes in impedance andgenerate IMD as a function of impedance presented at each carrierfrequency. Thus, implementing a front end system with switchedtermination can improve IMD performance of non-linear front endcomponents.

Additionally or alternatively to switched termination for transmitpaths, switched termination can be used for receive paths of the frontend system. For example, in certain embodiments, a front end systemincludes a frequency multiplexing circuit connected to a first RFreceive path and a second RF receive path. The front end system furtherincludes a switched termination circuit in shunt with the first RFreceive path and operable to turn on to suppress impedance variationwhen the first RF receive path is inactive.

FIG. 3A is a schematic diagram of a front end system 60 with switchedtermination according to one embodiment. The front end system 60includes a band switch 41, a frequency multiplexing circuit 42, acontrol circuit 45, and a switched termination circuit 51. Although oneembodiment of a front end system with a switched termination circuit isshown, the teachings herein are applicable to front end systemsimplemented in a wide variety of ways.

In the illustrated embodiment, the band switch 41 receives a band Atransmit signal (BAND A TX) and a band B transmit signal (BAND B TX).The band A transmit signal and band B transmit signal can correspond totransmit signals of a variety of frequency bands, including, but notlimited to, frequency bands specified by 3GPP, such as 4G, LTE, and/or5G bands. In the illustrated embodiment, the band switch 41 is atransmit band selection switch.

As shown in FIG. 3A, the band switch 41 further receives a band Aselection signal (SELA) and a band B selection signal (SELB) forselecting the band A transmit signal and the band B transmit signal,respectively.

Although an example in which the band switch 41 selects between twotransmit signals is shown, the band switch 41 can provide selectionamongst three or more signals. Furthermore, a state of a band switch canbe controlled in a wide variety of ways, including implementations usingmore or fewer selection signals.

The band switch 41 is coupled to the frequency multiplexing circuit 42via a first RF signal path 55 and a second RF signal path 56. When theband A transmit signal is selected, the band switch 41 provides the bandA transmit signal to the frequency multiplexing circuit 42 via the firstRF signal path 55. Additionally, when the band B transmit signal isselected, the band switch 41 provides the band B transmit signal to thefrequency multiplexing circuit 42 via the second RF signal path 56.

As shown in FIG. 3A, the frequency multiplexing circuit 42 is coupled toa bidirectional transmit/receive terminal (TX/RX), and outputs a band Areceive signal (BAND A RX) and a band B receive signal (BAND B RX). Thefrequency multiplexing circuit 42 can be implemented in a wide varietyof ways, including, but not limited to, using one or more duplexers, oneor more quadplexers, one or more switches, and/or other suitablecircuitry for multiplexing transmit and receive signals. Although theillustrated frequency multiplexing circuit 42 outputs two receivesignals, a frequency multiplexing circuit can be implemented to outputmore or fewer signals.

The frequency multiplexing circuit 42 can be used for multiplexing awide variety of types of signals, such as signals associated with FDDand/or TDD communications. In one example, band A and/or band B are usedfor communicating FDD signals associated with various carrieraggregation scenarios. In another example, band A and/or band B is usedfor communicating TDD signals, such as asynchronously operated TDDbands. For instance, asynchronous TDD can suffer from IP3considerations, for instance, +/−n*FDD₁+/−m*TDD₂=TDD₃, where TDD₂ andTDD₃ are asynchronous (mixed Tx and Rx timing) and TDD₃ corresponds tothe victim Rx band.

The illustrated embodiment includes the switched termination circuit 51,which is activated by a band A termination activation signal (SELA),which is controlled complementary to selection of the band A transmitsignal by the band A selection signal (SELA). Thus, when the band switch41 provides the band A transmit signal to the frequency multiplexer 42over the first RF signal path 55 such that the first RF signal path 55is active, the switched termination circuit 51 is turned off and doesnot provide termination. However, when the band A transmit signal is notprovided over the first RF signal path 55 such that the first RF signalpath 55 is inactive, the switched termination circuit 51 is turned on toprovide termination.

Thus, the switched termination circuit 51 turns on to provide impedancematching when the first RF signal path 55 is inactive. By including theswitched termination circuit 51, impedance matching at thetransmit/receive terminal (TX/RX) is provided, thereby enhancing IMDperformance of the front end system 60.

Although an example including one switched termination circuit isdepicted, a front end system can include multiple switched terminationcircuits. For example, the second RF signal path 56 can additionally oralternatively include a switched termination circuit that turns on toprovide impedance matching when the second RF signal path 56 isinactive. Furthermore, one or more additional RF signal paths can beincluded between the band switch 41 and the frequency multiplexingcircuit 42, and any number of the additional RF signal paths can includea switched termination circuit.

In the illustrated embodiment, the control circuit 45 generates the bandA selection signal (SELA), the band B selection signal (SELB), and theband A termination activation signal (SELA). In certain implementations,the control circuit 45 controls the state of the signals based on datareceived over a chip interface or bus.

FIG. 3B is a schematic diagram of a front end system 70 with switchedtermination according to another embodiment. The front end system 70includes a first switched termination circuit 51, a second switchedtermination circuit 52, a third switched termination circuit 53, a bandswitch 61, a frequency multiplexing circuit 62, an antenna switch 63, anantenna 64, a control circuit 65.

The front end system 70 of FIG. 3B is similar to the front end system 60of FIG. 3A, except that the band switch 61 and the frequencymultiplexing circuit 62 each operate over an additional frequency band(denoted by band C, in this example), with each RF signal path betweenthe band switch 61 and the frequency multiplexing circuit 62 including aswitched termination circuit in shunt with the RF signal path.Furthermore, the front end system 70 of FIG. 3B further includes theantenna switch 63 and the antenna 64.

Thus, the frequency multiplexing circuit 62 not only outputs the band Areceive signal (BAND A RX) and the band B receive signal (BAND B RX),but also the band C receive signal (BAND C RX). Furthermore, the bandswitch 61 receives not only the band A transmit signal (BAND A TX) andthe band B transmit signal (BAND B TX), but also the band C transmitsignal (BAND C TX). Moreover, the band switch 61 and the frequencymultiplexing circuit 62 are coupled by a first RF signal path 55, asecond RF signal path 56, and a third RF signal path 57, which areselectively terminated with the first switched termination circuit 51,the second switched termination circuit 52, and the third switchedtermination circuit 53, respectively.

Although an example operating over three frequency bands and using threeswitched termination circuits is shown, a front end system can operateover more or fewer frequency bands and/or include more or fewer switchedtermination circuits.

In the illustrated embodiment, the control circuit 65 generates the bandA selection signal (SELA), the band B selection signal (SELB), the bandC selection signal (SELC), the band A termination activation signal(SELA), the band B termination activation signal (SELB), and the band Ctermination activation signal (SELC). In certain implementations, thecontrol circuit 45 controls the state of the signals based on datareceived over a chip interface or bus.

FIG. 3C is a schematic diagram of a front end system 80 with switchedtermination according to another embodiment. The front end system 80includes a frequency multiplexing circuit 42, a control circuit 45, aswitched termination circuit 51, a first low noise amplifier (LNA) 71,and a second LNA 72. Although another embodiment of a front end systemwith a switched termination circuit is shown, the teachings herein areapplicable to front end systems implemented in a wide variety of ways.

As shown in FIG. 3C, the frequency multiplexing circuit 42 is coupled toa bidirectional transmit/receive terminal (TX/RX), and receives a band Atransmit signal (BAND A TX) and a band B transmit signal (BAND B TX).The frequency multiplexing circuit 42 can be implemented in a widevariety of ways, including, but not limited to, using one or moreduplexers, one or more quadplexers, one or more switches, and/or othersuitable circuitry for multiplexing transmit and receive signals.Although the illustrated frequency multiplexing circuit 42 receive twotransmit signals, a frequency multiplexing circuit can be implemented toreceive more or fewer transmit signals.

The frequency multiplexing circuit 42 can be used for multiplexing awide variety of types of signals, such as signals associated with FDDand/or TDD communications. In one example, band A and/or band B are usedfor communicating FDD signals associated with various carrieraggregation scenarios. In another example, band A and/or band B is usedfor communicating TDD signals, such as asynchronously operated TDDbands.

In the illustrated embodiment, the frequency multiplexing circuit 42 isalso coupled to the first LNA 71 over a first RF signal path 75, and tothe second LNA 72 over a second RF signal path 76. As shown in FIG. 3C,the first LNA 71 receives a band A selection signal (SELA) for enablingthe first LNA 71. When enabled, the first LNA 71 amplifies the RF signalon the first RF signal path 75 to generate a band A receive signal (BANDA RX). Additionally, the second LNA 72 receives a band B selectionsignal (SELB) for enabling the second LNA 72. When enabled, the secondLNA 72 amplifies the RF signal on the second RF signal path 76 togenerate a band B receive signal (BAND B RX).

The band A receive signal and band B receive signal can correspond totransmit signals of a variety of frequency bands, including, but notlimited to, frequency bands specified by 3GPP, such as 4G, LTE, and/or5G bands.

The illustrated embodiment includes the switched termination circuit 51,which is activated by a band A termination activation signal (SELA),which is controlled complementary to the band A selection signal (SELA).Thus, when the first LNA 71 is enabled, the switched termination circuit51 is turned off and does not provide termination. However, when thefirst LNA 71 is disabled, the switched termination circuit 51 is turnedon to provide termination.

Thus, the switched termination circuit 51 turns on to provide impedancematching when the first RF signal path 75 is inactive. By including theswitched termination circuit 51, impedance matching at thetransmit/receive terminal (TX/RX) is provided, thereby enhancing IMDperformance of the front end system 80.

Although an example including one switched termination circuit isdepicted, a front end system can include multiple switched terminationcircuits. For example, the second RF signal path 76 can additionally oralternatively include a switched termination circuit that turns on toprovide impedance matching when the second RF signal path 76 isinactive. Furthermore, one or more additional RF signal paths can beincluded, and any number of the additional RF signal paths can include aswitched termination circuit.

FIG. 3D is a schematic diagram of a front end system 90 with switchedtermination according to another embodiment. The front end system 90includes a first switched termination circuit 51, a second switchedtermination circuit 52, a third switched termination circuit 53, afrequency multiplexing circuit 62, an antenna switch 63, an antenna 64,a control circuit 65, a first LNA 71, a second LNA 72, and a third LNA73.

The front end system 90 of FIG. 3D is similar to the front end system 80of FIG. 3C, except that the front end system 90 further includes theantenna switch 63 and the antenna 64, and the frequency multiplexingcircuit 62 operates over an additional frequency band (denoted by bandC, in this example).

Thus, the frequency multiplexing circuit 62 receives a band C transmitsignal (BAND C TX) and is coupled to the third LNA 73 over a third RFsignal path 77. The third LNA 73 is controlled by a band C selectionsignal (SELC), and outputs a band C receive signal (BAND C RX) whenenabled. The first RF signal path 75, the second RF signal path 76, andthe third R signal path 77 are selectively terminated by the firstswitched termination circuit 51, the second switched termination circuit52, and the third switched termination circuit 53, respectively.

Although an example operating over three frequency bands and using threeswitched termination circuits is shown, a front end system can operateover more or fewer frequency bands and/or include more or fewer switchedtermination circuits.

FIG. 3E is a schematic diagram of a front end system 100 with switchedtermination according to another embodiment. The front end system 100includes a frequency multiplexing circuit 42, a control circuit 45, aswitched termination circuit 51, and an LNA switch 91.

The front end system 100 of FIG. 3E is similar to the front end system80 of FIG. 3C, except that the front end system 100 omits the first LNA71 and the second LNA 72 and includes the LNA switch 91. The LNA switch91 is also referred to herein as a receive switch.

In the illustrated embodiment, the LNA switch 91 outputs a band Areceive signal (BAND A RX) when the band A selection signal (SELA) isactive, and outputs a band B receive signal (BAND B RX) when the band Bselection signal (SELB) is active. In certain implementations, the bandA receive signal (BAND A RX) and the band B receive signal (BAND B RX)are provided to a common or shared LNA, thereby reducing amplifieroverhead and component count relative to an implementation including aseparate LNA for each path.

The switched termination circuit 51 activates when the first RF signalpath 75 is inactive. By including the switched termination circuit 51,impedance matching at the transmit/receive terminal (TX/RX) is provided,thereby enhancing IMD performance of the front end system 100.

Although an example with two RF receive paths and one switchedtermination circuits is shown, addition RF receive paths and/or switchedtermination circuits can be included.

FIG. 4A is a schematic diagram of a front end system 140 with switchedtermination according to another embodiment. The front end system 140includes a power amplifier 81, a band switch 82, a B1 LNA 83, a B3 LNA84, a B1 duplexer 85, a B3 duplexer 86, a matching inductor 87, anantenna switch 88 (implemented on an SOI die, in this example), a B1switched termination circuit 89, a B3 switched termination circuit 90, aB1 decoupling switch 96, a B3 decoupling switch 97, a first shuntgrounding switch 101, a second shunt grounding switch 102, a third shuntgrounding switch 103, a fourth shunt grounding switch 104, a fifth shuntgrounding switch 105, a first low impedance element 111, a second lowimpedance element 112, a third low impedance element 113, a fourth lowimpedance element 114, and a fifth low impedance element 115.

As shown in FIG. 4A, an output of the power amplifier 81 is coupled to amid band (MB) input of the band switch 82. The band switch 82 includes aB34/39 selection switch 131, a B1 selection switch 132, another B1selection switch 133, a B2 selection switch 134, and a B3 selectionswitch 135. In the illustrated embodiment, the power amplifier 81 isshared across multiple frequency bands, thereby reducing cost, area,and/or complexity. However, in other implementations, two or more poweramplifiers can be included.

The B1 switched termination 89 includes a shunt switch 121 and atermination resistor 125, which in certain implementations is about 50ohms. The shunt switch 121 is opened when the B1 transmit signal path137 is active and closed when the B1 transmit signal path 137 isinactive.

The B3 switched termination 90 includes a shunt switch 122 and atermination resistor 126, which in certain implementations is about 50ohms. The shunt switch 122 is opened when the B3 transmit signal path138 is active and closed when the B3 transmit signal path 138 isinactive.

Including the B1 switched termination circuit 89 and B3 switchedtermination circuit 90 improves impedance matching relative to animplementation in which the switched termination circuits are omitted.For example, impedance matching at node 139 (corresponding to abidirectional TX/RX node) can be enhanced by terminating the B1 transmitsignal path 137 when B1 transmission is inactive, and by terminating theB3 transmit signal path 138 when B3 transmission is inactive.

Accordingly, the B1 switched termination circuit 89 operates to preserveimpedance to be substantially constant (for instance, about 50 ohms) atthe B1 transmit frequencies at node 139, while the B3 switchedtermination circuit 90 operates to preserve impedance to besubstantially constant at the B3 transmit frequencies at node 139.

In certain implementations herein, a switched termination circuitoperates to terminate a signal path associated with a frequency bandacross a frequency range of the band. For example, the switchedtermination circuit can maintain impedance substantially constant forsignal frequencies within the frequency band.

The front end system 140 of FIG. 4A further includes the groundingswitches 101-105 and low impedance elements 111-115, which are used toshunt unused ports or terminals of the band switch 82 to ground, therebyproviding high isolation. Additionally, the B1 decoupling switch 96 andthe B3 decoupling switch 97 are included, which have relatively lowinsertion loss for signaling performance while achieving sufficientisolation.

By including both grounding switches and switched termination circuits,both high isolation and robust IMD performance can be achieved.

For example, although the termination resistors 125-126 provide goodsuppression of impedance variation, the resistance of the terminationresistors 125-126 may be too high to provide good isolation of theblocker frequency to the output of the power amplifier 81 (for instance,a collector of a bipolar transistor or a drain of a field-effecttransistor). Thus, including both the termination resistors 125-126 forproviding termination and the grounding switches 101-105 for providingisolation can reduce or eliminate a tradeoff between isolation and IMDperformance.

In the illustrated embodiment, switched termination circuits are used toenhance performance of a front end system that communicates in partusing B1 and B3. For example, the front end system 140 can suffer from aB1+B3 uplink carrier aggregation scenario having a third order IMDsensitivity consideration of 2*B1_(TX)×B3_(TX)=B1_(RX), where one ofB1_(TX) or B3_(TX) is from the power amplifier 81 and the other is froma satellite power amplifier (see for example, the configuration of FIG.8).

Although an example of a front end system operating over specificexamples of frequency bands is shown, the teachings herein areapplicable to RF front ends operating over a wide variety of frequencybands. Accordingly, other implementations are possible.

FIG. 4B is a schematic diagram of a front end system 150 with switchedtermination according to another embodiment. The front end system 150includes a power amplifier 81, a band switch 82, a B1 LNA 83, a B3 LNA84, a B1 duplexer 85, a B3 duplexer 86, a matching inductor 87, anantenna switch 88 (implemented on an SOI die, in this example), a firstB1 switched termination circuit 89, a first B3 switched terminationcircuit 90, a B1 decoupling switch 96, a B3 decoupling switch 97, firstto fifth shunt grounding switches 101-105, respectively, first to fifthlow impedance elements 111-115, respectively, a second B1 switchedtermination circuit 151, and a second B3 switched termination circuit152.

The front end system 150 of FIG. 4B is similar to the front end system140 of FIG. 4A, except that the front end system 150 further includesthe second B1 switched termination circuit 151 and the second B3switched termination circuit 152.

When the B1 LNA 83 is enabled, the second B1 switched terminationcircuit 151 is disabled. However, when the B1 LNA 83 is disabled, thesecond B1 switched termination circuit 151 is enabled to terminate theinput of the B1 LNA 83. Additionally, when the B3 LNA 84 is enabled, thesecond B3 switched termination circuit 152 is disabled. However, whenthe B3 LNA 84 is disabled, the second B3 switched termination circuit152 is enabled to terminate the input of the B3 LNA 84.

FIG. 5A is one example of a Smith chart for a front end system withoutswitched termination. The Smith chart corresponds to simulations of oneimplementation of the front end system 140 of FIG. 4A in which the B1switched termination circuit 89 and the B3 switched termination circuit90 are omitted. The Smith chart provides a graphical illustrated ofimpedance at node 139 at the input of the antenna switch 88 for animplementation without switched termination.

As shown by the relatively loose contour of FIG. 5A, the impedance isrelatively uncontrolled. For example, approximately 0 ohms at terminalB3 of FIG. 4A and a relatively high phase shift versus frequency of theB3 duplexer 86 results in uncontrolled impedance at the node 139. SinceIMD can be relative high at high impedance values and relatively low atlow impedance values, the IMD performance of the front end systemassociated with FIG. 5A can fluctuate relatively greatly.

FIG. 5B is one example of a Smith chart for a front end system withswitched termination. The Smith chart corresponds to simulations of oneimplementation of the front end system 140 of FIG. 4A in which the B1switched termination circuit 89 and the B3 switched termination circuit90 are included. As shown by a comparison of FIGS. 5A and 5B, the Smithchart of FIG. 5B corresponds to a tighter contour and more tightlycontrolled impedance. Thus, the Smith chart of FIG. 5B is associatedwith superior IMD performance relative to the Smith chart of FIG. 5A.

FIG. 6 is a schematic diagram of a front end system 200 with switchedtermination according to another embodiment. The front end system 200includes a band switch 181, a frequency multiplexing circuit 182, anantenna switch 183, a switched termination circuit 184, a matchinginductor 185, a grounding switch 191, and a decoupling switch 192. Theswitched termination circuit 184 includes a shunt switch 193 and atermination resistor 194, which can be substantially 50 ohms or otherdesired termination impedance value.

The frequency multiplexing circuit 182 includes a B1 duplexer 186, a B3duplexer 187, a B4 duplexer 188, a B1 phase shifter 189, and a B3 phaseshifter 190. Although one example of a frequency multiplexing circuit isshown, other implementations are possible, such as configurations usinga quadplexer and/or other suitable multiplexing circuitry.

The illustrated band switch 181 receives a B1 transmit signal (B1 TX),which the band switch 181 selectively provides to the frequencymultiplexing circuit 182 over a B1 transmit signal path 197.Additionally, the band switch 181 receives a B3 transmit signal (B3 TX),which the band switch 181 selectively provides to the frequencymultiplexing circuit 182 over a B3 transmit signal path 198.

Including the switched termination circuit 184 preserves impedancematching at the node 199, even when the grounding switch 191 is closedto provide good isolation. Accordingly, isolation can be achieved whilemaintaining high IMD performance.

FIG. 7A is a schematic diagram of one embodiment of a switchconfiguration 260 for a terminal of a band switch. The switchconfiguration 260 includes a switched termination circuit 250, a bandselection switch 251, a decoupling switch 252, and a grounding switch253. The switched termination circuit 250 includes a shunt switch 254and a termination resistor 255, which is about 50 ohm in certainimplementations.

When the band selection switch 251 and the decoupling switch 252 areclosed and the grounding switch 253 and shunt switch 254 are opened, atransmit input signal (TX IN) propagates through the switchconfiguration 260 to thereby provide a transmit output signal (TX OUT).However, when the band selection switch 251 and the decoupling switch252 are opened and the grounding switch 253 and shunt switch 254 areclosed, the transmit input signal does not propagate through the switchconfiguration 260. Rather, the grounding switch 253 provides groundingfor high isolation and the switched termination circuit 250 providedimpedance matching for good IMD performance.

Accordingly, the illustrated switch configuration 260 provides both highisolation and good IMD performance.

FIG. 7B is a schematic diagram of another embodiment of a switchconfiguration 270 for a terminal of a band switch. The switchconfiguration 270 of FIG. 7B is similar to the switch configuration 260of FIG. 7A, except that the decoupling switch 252 and the groundingswitch 253 are omitted. The switch configuration 270 of FIG. 7B providespoorer isolation but lower complexity relative to the switchconfiguration 260 of FIG. 7A.

FIG. 8 is a schematic diagram of a front end system 460 with switchedtermination according to another embodiment. The front end system 460includes a primary transmit and receive (TX/RX) module 401, a secondarytransmit (TX) module 402, a diversity/MIMO module 403, a primarytriplexer 404, a diversity triplexer 405, a primary antenna 407, and adiversity antenna 408.

As shown in FIG. 8, the primary TX/RX module 401 includes a poweramplifier 411, a transmit band selection switch 412 implemented withswitched termination, a first receive band selection switch 413, asecond receive band selection switch 414, a B1+B3 quadplexer 421, aB2+B66 quadplexer 422, and an antenna switch 423.

Additionally, the secondary TX module 401 includes a power amplifier431, a transmit band selection switch 432 implemented with switchedtermination, and a quadplexer 433.

Furthermore, the diversity/MIMO module 403 includes a first LNA 441, asecond LNA 442, an LNA switch 443, an antenna switch 444, a first filter451, a second filter 452, a third filter 453, and a fourth filter 454.

The front end system 460 communicates over a wide variety of frequencybands, including those associated with low band (LB), mid band (MB), andhigh band (HB) frequency ranges. For example, LB signals can have afrequency content of 1 GHz or less, MB signals can have a frequencycontent between 1 GHz and 2.3 GHz, and HB signals can have a frequencycontent of 2.3 GHz or higher. Examples of LB frequencies include, butare not limited to Band 8, Band 20, and Band 26. Examples of MBfrequencies include, but are not limited to, Band 1, Band 2, Band 3,Band 4, and Band 66. Examples of HB frequencies include, but are notlimited to, Band 7, Band 38, and Band 41.

The illustrated end system 460 operates with finite isolation 459between the primary antenna 407 and the diversity antenna 408. In thisembodiment, the power amplifier 431 transmits via the diversity antenna408 and the power amplifier 411 transmits via the primary antenna 407.Transmitting by separate antennas can enhance performance for difficultuplink carrier aggregation scenarios by reducing IMD. The linearity ofan antenna switch (for instance, the antenna switch 423 and/or theantenna switch 444) can limit a receive sensitivity of the front endsystem 460.

By implementing the transmit band selection switch 412 and the transmitband selection switch 432 with switched termination circuits, thelinearity of the antenna switch 423 and the antenna switch 444 isimproved. Thus, the front end system 460 can operate with enhancedperformance, including, but not limited to, higher receive sensitivity.

Although one embodiment of a front end system with switched terminationcircuits is shown, the teachings herein are applicable to front endsystems implemented in a wide variety of ways.

FIG. 9 is a schematic diagram of one embodiment of a mobile device 800.The mobile device 800 includes a baseband system 801, a transceiver 802,a front end system 803, antennas 804, a power management system 805, amemory 806, a user interface 807, and a battery 808.

The mobile device 800 can be used communicate using a wide variety ofcommunications technologies, including, but not limited to, 2G, 3G, 4G(including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (forinstance, WiFi), WPAN (for instance, Bluetooth and ZigBee), WMAN (forinstance, WiMax), and/or GPS technologies.

The transceiver 802 generates RF signals for transmission and processesincoming RF signals received from the antennas 804. It will beunderstood that various functionalities associated with the transmissionand receiving of RF signals can be achieved by one or more componentsthat are collectively represented in FIG. 9 as the transceiver 802. Inone example, separate components (for instance, separate circuits ordies) can be provided for handling certain types of RF signals.

The front end system 803 aids is conditioning signals transmitted toand/or received from the antennas 804. In the illustrated embodiment,the front end system 803 includes antenna tuning circuitry 810, poweramplifiers (PAs) 811, low noise amplifiers (LNAs) 812, filters 813,switches 814, and signal splitting/combining circuitry 815. However,other implementations are possible.

For example, the front end system 803 can provide a number offunctionalities, including, but not limited to, amplifying signals fortransmission, amplifying received signals, filtering signals, switchingbetween different bands, switching between different power modes,switching between transmission and receiving modes, duplexing ofsignals, multiplexing of signals (for instance, diplexing ortriplexing), or some combination thereof.

In certain implementations, the mobile device 800 supports carrieraggregation, thereby providing flexibility to increase peak data rates.Carrier aggregation can be used for both Frequency Division Duplexing(FDD) and Time Division Duplexing (TDD), and may be used to aggregate aplurality of carriers or channels. Carrier aggregation includescontiguous aggregation, in which contiguous carriers within the sameoperating frequency band are aggregated. Carrier aggregation can also benon-contiguous, and can include carriers separated in frequency within acommon band or in different bands.

The antennas 804 can include antennas used for a wide variety of typesof communications. For example, the antennas 804 can include antennasfor transmitting and/or receiving signals associated with a wide varietyof frequencies and communications standards.

In certain implementations, the antennas 804 support MIMO communicationsand/or switched diversity communications. For example, MIMOcommunications use multiple antennas for communicating multiple datastreams over a single radio frequency channel. MIMO communicationsbenefit from higher signal to noise ratio, improved coding, and/orreduced signal interference due to spatial multiplexing differences ofthe radio environment. Switched diversity refers to communications inwhich a particular antenna is selected for operation at a particulartime. For example, a switch can be used to select a particular antennafrom a group of antennas based on a variety of factors, such as anobserved bit error rate and/or a signal strength indicator.

The mobile device 800 can operate with beamforming in certainimplementations. For example, the front end system 803 can includeamplifiers having controllable gain and phase shifters havingcontrollable phase to provide beam formation and directivity fortransmission and/or reception of signals using the antennas 804. Forexample, in the context of signal transmission, the amplitude and phasesof the transmit signals provided to the antennas 804 are controlled suchthat radiated signals from the antennas 804 combine using constructiveand destructive interference to generate an aggregate transmit signalexhibiting beam-like qualities with more signal strength propagating ina given direction. In the context of signal reception, the amplitude andphases are controlled such that more signal energy is received when thesignal is arriving to the antennas 804 from a particular direction. Incertain implementations, the antennas 804 include one or more arrays ofantenna elements to enhance beamforming.

The baseband system 801 is coupled to the user interface 807 tofacilitate processing of various user input and output (I/O), such asvoice and data. The baseband system 801 provides the transceiver 802with digital representations of transmit signals, which the transceiver802 processes to generate RF signals for transmission. The basebandsystem 801 also processes digital representations of received signalsprovided by the transceiver 802. As shown in FIG. 9, the baseband system801 is coupled to the memory 806 of facilitate operation of the mobiledevice 800.

The memory 806 can be used for a wide variety of purposes, such asstoring data and/or instructions to facilitate the operation of themobile device 800 and/or to provide storage of user information.

The power management system 805 provides a number of power managementfunctions of the mobile device 800. In certain implementations, thepower management system 805 includes a PA supply control circuit thatcontrols the supply voltages of the power amplifiers 811. For example,the power management system 805 can be configured to change the supplyvoltage(s) provided to one or more of the power amplifiers 811 toimprove efficiency, such as power added efficiency (PAE).

As shown in FIG. 9, the power management system 805 receives a batteryvoltage from the battery 808. The battery 808 can be any suitablebattery for use in the mobile device 800, including, for example, alithium-ion battery.

Applications

Some of the embodiments described above have provided examples inconnection with mobile devices. However, the principles and advantagesof the embodiments can be used for any other systems or apparatus thathave needs for front end systems with enhanced intermodulationdistortion (IMD) performance. Examples of such RF communication systemsinclude, but are not limited to, mobile phones, tablets, base stations,network access points, customer-premises equipment (CPE), laptops, andwearable electronics.

CONCLUSION

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Likewise, the word “connected”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

1. A front end system comprising: a frequency multiplexing circuit; aband switch configured to selectively provide the frequency multiplexingcircuit with a first transmit signal over a first radio frequency signalpath and with a second transmit signal over a second radio frequencysignal path; and a first switched termination circuit in shunt with thefirst radio frequency signal path and operable to turn on to suppressimpedance variation when the first radio frequency signal path isinactive.
 2. The front end system of claim 1 further comprising a secondswitched termination circuit in shunt with the second radio frequencysignal path and operable to turn on to suppress impedance variation whenthe second radio frequency signal path is inactive.
 3. The front endsystem of claim 1 further comprising an antenna switch coupled to thefrequency multiplexing circuit at a node, the first switched terminationcircuit operable to maintain impedance matching at the node over asignal frequency range of the first transmit signal.
 4. The front endsystem of claim 1 wherein the frequency multiplexing circuit is furtherconfigured to output a first receive signal and a second receive signal.5. The front end system of claim 1 wherein the frequency multiplexingcircuit includes at least one duplexer.
 6. The front end system of claim1 wherein the band switch provides the first radio frequency signal atan output terminal, the front end system further comprising a groundingswitch electrically connected between the output terminal and ground. 7.The front end system of claim 6 further comprising a decoupling switchelectrically connected between the output terminal of the band switchand the first switched termination circuit.
 8. The front end system ofclaim 1 wherein the first switched termination circuit includes a shuntswitch and a termination resistor electrically connected in series. 9.The front end system of claim 8 wherein the termination resistor has aresistance of about fifty ohms.
 10. The front end system of claim 1wherein the band switch is further configured to selectively provide thefrequency multiplexing circuit with a third transmit signal over a thirdradio frequency signal path.
 11. The front end system of claim 1 furthercomprising a power amplifier configured to provide the band switch withthe first transmit signal and the second transmit signal at an inputterminal to the band switch.
 12. A mobile device comprising: atransceiver configured to generate at least one radio frequency signal;and a front end system configured to process the at least one radiofrequency signal from the transceiver to generate a first transmitsignal and a second transmit signal, the front end system including afrequency multiplexing circuit and a band switch configured toselectively provide the frequency multiplexing circuit with the firsttransmit signal over a first radio frequency signal path and with thesecond transmit signal over a second radio frequency signal path, thefront end system further including a first switched termination circuitin shunt with the first radio frequency signal path and operable to turnon to suppress impedance variation when the first radio frequency signalpath is inactive.
 13. The mobile device of claim 12 wherein the frontend system further includes a second switched termination circuit inshunt with the second radio frequency signal path and operable to turnon to suppress impedance variation when the second radio frequencysignal path is inactive.
 14. The mobile device of claim 12 wherein thefront end system further includes an antenna switch coupled to thefrequency multiplexing circuit at a node, the first switched terminationcircuit operable to maintain impedance matching at the node over asignal frequency range of the first transmit signal.
 15. The mobiledevice of claim 14 further comprising a first antenna, the antennaswitch operable to selectively connect the node to the first antenna.16. The mobile device of claim 12 wherein the front end system furtherincludes at least one power amplifier configured to generate the firsttransmit signal and the second transmit signal.
 17. The mobile device ofclaim 12 wherein the band switch provides the first radio frequencysignal at an output terminal, the front end system further including agrounding switch electrically connected between the output terminal andground.
 18. The mobile device of claim 17 wherein the front end systemfurther includes a decoupling switch electrically connected between theoutput terminal of the band switch and the first switched terminationcircuit.
 19. A method of radio frequency signal communication, themethod comprising: controlling a state of a band switch to provide afirst transmit signal to a frequency multiplexing circuit over a firstradio frequency signal path; changing the state of the band switch todeactivate the first radio frequency signal path and to provide a secondtransmit signal to the frequency multiplexing circuit over a secondradio frequency signal path; and turning on a first switched terminationcircuit in shunt to the first radio frequency signal path to suppressimpedance variation when the first radio frequency signal path isdeactivated.
 20. The method of claim 19 further comprising maintainingimpedance matching at a node between the frequency multiplexing circuitand an antenna switch over a signal frequency range of the firsttransmit signal. 21-60. (canceled)